Study On Drainage Behavior Of CO₂ Oil-water Mixed Foam

In the process of CO₂ foam flooding and oil field gathering and transportation,CO₂ foam contacts with crude oil,and a large amount of CO₂ oil-water mixed foam is formed under the action of surface active substances.Foam stability is needed in the process of mining,and foam collapse is needed in the gathering and transportation system.In the separator,the foam needs to collapse quickly,and the drainage behavior is an important factor in the stability of the foam.The research on the drainage behavior of the CO₂ oil-water mixed foam is of great significance to ensure the efficient operation of the separator.In this paper,the effects of different factors on the characteristics and drainage behavior of CO₂ oil-water mixed foam are explored by means of experiment and molecular dynamics simulation,and the prediction model of CO₂ oil-water mixed foam drainage is proposed to quantify the drainage behavior,and the action mechanism of oil phase molecules on drainage was put forward from the molecular point of view.The main work of this paper is as follows:（1）The effects of surfactants and oil phase molecules on foam characteristics were studied,and the results showed that:The foam produced by SDS as surfactant has good oil stain resistance.Oil phase molecules inhibit foam formation.The foaming performance will get better with the increase of surfactant concentration.When the concentration of surfactant is high,the stability of foam can be improved by oil phase molecules.In foam flooding,the surfactant concentration can be properly increased to improve the oil pollution resistance of foam.In the gathering and transportation system,if the concentration of surfactant is high,a stable oil-water mixed foam will be formed,which will affect the operation of the gathering and transportation system.（2）The drainage behavior of CO₂ oil-water mixed foam was studied from the aspects of top foam,bottom foam and drainage volume by means of electrical conductivity method,macroscopic observation and microscopic observation.The formula of top foam discharge was obtained.The increase of the content of oil phase molecules can inhibit the drainage.From the microscopic observation results,the oil phase molecules form a solid oil film in the liquid film,which hinders the liquid flow in the liquid film,thus inhibiting the drainage behavior.The order of the factors affecting the drainage of CO₂ oil-water mixed foam is as follows:p H>oil phase content>surfactant concentration>salt content.（3）Through derivation,a CO₂ oil-water mixed foam drainage model is proposed.The model divides the drainage behavior into two stages,and this model can be used to describe the foam drainage process.（4）Through the study of the motion behavior of oil phase molecules and water molecules in the liquid film,it is concluded that:The velocity of liquid discharge increases gradually in the early stage of liquid discharge,because the oil phase molecules in the foam system move into the surfactant layer,and the hindrance of liquid discharge decreases gradually.In the later stage of liquid discharge,the discharge speed gradually decreases because the foam liquid film becomes thinner and the binding effect of surfactant on water molecules increases.